Relationship between oral declaration on adherence to ivermectin treatment and parasitological indicators of onchocerciasis in an area of persistent transmission despite a decade of mass drug administration in Cameroon.

Bottom Line:
There was a treatment-dependent reduction in microfilaria prevalence (rs =-0.986, P = 0.01) and intensity (rs =-0.96, P = 0.01).The highest mf prevalence (59.7%) was found in the zero treatment group and the lowest (33.9%) in the ≥ 7 times treatment group (OR = 2.8; 95% CI [2.09-3.74]; P < 0.001).Our findings show that using parasitological indicators, reduction in prevalence is IVM intake-dependent and that participants' oral declaration of treatment adherence could be relied upon for impact studies.

Affiliation: Parasite and Vectors Research Unit, Department of Microbiology and Parasitology, University of Buea, P.O.Box 63, Buea, Cameroon. swanji@yahoo.fr.

ABSTRACT

Background: Onchocerciasis control for years has been based on mass drug administration (MDA) with ivermectin (IVM). Adherence to IVM repeated treatment has recently been shown to be a confounding factor for onchocerciasis elimination precisely in rain forest areas where transmission continues and Loa loa co-exists with Onchocerca volvulus. In this study, participants' oral declarations were used as proxy to determine the relationship between adherence to IVM treatment and parasitological indicators of onchocerciasis in the rain forest area of Cameroon with more than a decade of MDA.

Methods: Participants were recruited based on their IVM intake profile with the aid of a semi-structured questionnaire. Parasitological examinations (skin sniping and nodule palpation) were done on eligible candidates. Parasitological indicators were calculated and correlated to IVM intake profile.

Results: Of 2,364 people examined, 15.5% had never taken IVM. The majority (40.4%) had taken the drug 1-3 times while only 18% had taken ≥ 7 times. Mf and nodule prevalence rates were still high at 47%, 95% CI [44.9-49.0%] and 36.4%, 95% CI [34.4-38.3%] respectively. There was a treatment-dependent reduction in microfilaria prevalence (rs =-0.986, P = 0.01) and intensity (rs =-0.96, P = 0.01). The highest mf prevalence (59.7%) was found in the zero treatment group and the lowest (33.9%) in the ≥ 7 times treatment group (OR = 2.8; 95% CI [2.09-3.74]; P

Conclusion: Adherence to ivermectin treatment is not adequate in this rain forest area where L. loa co-exists with O. volvulus. The prevalence and intensity of onchocerciasis remained high in individuals with zero IVM intake after more than a decade of MDA. Our findings show that using parasitological indicators, reduction in prevalence is IVM intake-dependent and that participants' oral declaration of treatment adherence could be relied upon for impact studies. The findings are discussed in the context of challenges for the elimination of onchocerciasis in this rain forest area.

Fig6: Changes in the proportions of study population in defined mf load groups in relation to IVM intake profile. (Number of people examined per IVM intake groups: [0 time] = 367; [1-3 times] = 956; [4-6 times] =615; [≥7 times] =426). P-value given for each defined mf load group and significance level set at 5 %

Mentions:
Like with mf prevalence, no association with trend was found between IVM intake and the proportion of individuals with different mf loads for children (Fig. 4). However, the proportion of people with no microfilariae in the skin was found to increase with IVM intake in adults and overall study population (Figs. 5 and 6). Of the 285 (15.1 %) adults who had never taken the drug, 40.0 % had no microfilaria. This proportion gradually increased with IVM intake to 66.6 % for those who had taken the drug 7 times and above (Fig. 5, P < 0.0001). Logistic regression revealed that adults who had had IVM 7 times or more were 2.99 times more likely to have individuals with no mf compared to the zero IVM intake group (OR = 2.99; 95 % IC [2.19–4.08], P < 0.0001; Table 5). The opposite was observed with infected individuals (Fig. 5). The proportion of individuals with mf load ranging from 1–50 mf/ss decreased from 50.9 % in the untreated group to 31.7 % in the ≥7 treatment round groups (OR = 0.45; 95 % IC [0.33–0.61], P < 0.0001; Table 5). The same trend was observed with [51–100 mf] and [>100 mf] groups (OR = 0.15; 95 % IC [0.05–0.45], P = 0.001; and OR = 0.22; 95 % IC [0.06–0.82], P = 0.025, respectively; Table 5; Fig. 5). This relationship was also found with the entire study population (Table 6; Fig. 6) but not with children (Fig. 4).Fig. 4

Relationship between oral declaration on adherence to ivermectin treatment and parasitological indicators of onchocerciasis in an area of persistent transmission despite a decade of mass drug administration in Cameroon.

Fig6: Changes in the proportions of study population in defined mf load groups in relation to IVM intake profile. (Number of people examined per IVM intake groups: [0 time] = 367; [1-3 times] = 956; [4-6 times] =615; [≥7 times] =426). P-value given for each defined mf load group and significance level set at 5 %

Mentions:
Like with mf prevalence, no association with trend was found between IVM intake and the proportion of individuals with different mf loads for children (Fig. 4). However, the proportion of people with no microfilariae in the skin was found to increase with IVM intake in adults and overall study population (Figs. 5 and 6). Of the 285 (15.1 %) adults who had never taken the drug, 40.0 % had no microfilaria. This proportion gradually increased with IVM intake to 66.6 % for those who had taken the drug 7 times and above (Fig. 5, P < 0.0001). Logistic regression revealed that adults who had had IVM 7 times or more were 2.99 times more likely to have individuals with no mf compared to the zero IVM intake group (OR = 2.99; 95 % IC [2.19–4.08], P < 0.0001; Table 5). The opposite was observed with infected individuals (Fig. 5). The proportion of individuals with mf load ranging from 1–50 mf/ss decreased from 50.9 % in the untreated group to 31.7 % in the ≥7 treatment round groups (OR = 0.45; 95 % IC [0.33–0.61], P < 0.0001; Table 5). The same trend was observed with [51–100 mf] and [>100 mf] groups (OR = 0.15; 95 % IC [0.05–0.45], P = 0.001; and OR = 0.22; 95 % IC [0.06–0.82], P = 0.025, respectively; Table 5; Fig. 5). This relationship was also found with the entire study population (Table 6; Fig. 6) but not with children (Fig. 4).Fig. 4

Bottom Line:
There was a treatment-dependent reduction in microfilaria prevalence (rs =-0.986, P = 0.01) and intensity (rs =-0.96, P = 0.01).The highest mf prevalence (59.7%) was found in the zero treatment group and the lowest (33.9%) in the ≥ 7 times treatment group (OR = 2.8; 95% CI [2.09-3.74]; P < 0.001).Our findings show that using parasitological indicators, reduction in prevalence is IVM intake-dependent and that participants' oral declaration of treatment adherence could be relied upon for impact studies.

Affiliation:
Parasite and Vectors Research Unit, Department of Microbiology and Parasitology, University of Buea, P.O.Box 63, Buea, Cameroon. swanji@yahoo.fr.

ABSTRACT

Background: Onchocerciasis control for years has been based on mass drug administration (MDA) with ivermectin (IVM). Adherence to IVM repeated treatment has recently been shown to be a confounding factor for onchocerciasis elimination precisely in rain forest areas where transmission continues and Loa loa co-exists with Onchocerca volvulus. In this study, participants' oral declarations were used as proxy to determine the relationship between adherence to IVM treatment and parasitological indicators of onchocerciasis in the rain forest area of Cameroon with more than a decade of MDA.

Methods: Participants were recruited based on their IVM intake profile with the aid of a semi-structured questionnaire. Parasitological examinations (skin sniping and nodule palpation) were done on eligible candidates. Parasitological indicators were calculated and correlated to IVM intake profile.

Results: Of 2,364 people examined, 15.5% had never taken IVM. The majority (40.4%) had taken the drug 1-3 times while only 18% had taken ≥ 7 times. Mf and nodule prevalence rates were still high at 47%, 95% CI [44.9-49.0%] and 36.4%, 95% CI [34.4-38.3%] respectively. There was a treatment-dependent reduction in microfilaria prevalence (rs =-0.986, P = 0.01) and intensity (rs =-0.96, P = 0.01). The highest mf prevalence (59.7%) was found in the zero treatment group and the lowest (33.9%) in the ≥ 7 times treatment group (OR = 2.8; 95% CI [2.09-3.74]; P

Conclusion: Adherence to ivermectin treatment is not adequate in this rain forest area where L. loa co-exists with O. volvulus. The prevalence and intensity of onchocerciasis remained high in individuals with zero IVM intake after more than a decade of MDA. Our findings show that using parasitological indicators, reduction in prevalence is IVM intake-dependent and that participants' oral declaration of treatment adherence could be relied upon for impact studies. The findings are discussed in the context of challenges for the elimination of onchocerciasis in this rain forest area.